Nissan Altima Wont Go Over 20 MPH: Let’s Find Out The Reasons

It’s a frustrating and even dangerous scenario – you’re driving along in your Nissan Altima, and suddenly, it bogged down and struggled to go over 20 mph. 

No matter how hard you press the gas, the car lacks power. 

If this happens to you, don’t panic! By methodically troubleshooting a few key systems, you can get to the bottom of the acceleration issues.

Diagnosing The Altima’s Acceleration Problems

• When an Altima won’t accelerate properly, there are two main systems to address that could cause speed limitations:

Transmission Control Systems

• The transmission is responsible for shifting gears to increase the speed. 

• Faulty components here can throw some codes and cause acceleration problems.

Engine Control Systems

• The engine control unit and various sensors govern performances. 

• Insufficient data on this computer can also trigger the limp mode limits.

• By diagnosing codes and signals from both of these critical systems, you can uncover the issues that causes the 20 mph problem.

Common Codes That Are Pointing To The Acceleration Problems

• Connecting an OBD2 scanner and pulling diagnostic trouble codes is the first step towards diagnosing the poor Altima acceleration.

Faulty Transmission Control Codes

Two standard transmission codes are:

• P0725 – Engine Speed Sensor

• P1778 – Transmission Control System Defect

These indicates shows that the car’s computer is preventing the shifting capability into higher gears.

Check Engine Light

• The check engine light being illuminated also signifies problems with engine control sensors or performance limitations being activated.

Inspecting The Transmission Components

• With transmission codes in the display, thoroughly inspect the mechanical condition and fluid levels of the transmission first. 

• If worn parts or leaks are found here, repairs may be necessary.

Transmission Fluids

• Check the transmission fluid level and change the filters if contaminated or filled over the ideal capacity. 

• This is because bad fluid can cause the acceleration problems as well.

No Visible Damage? Investigate The Sensors

• If no visible transmission defects are present, acceleration issues are likely caused by electrical problems and mechanical failures.

Digging Into The Engine’s Control Unit Sensor Data

• Access the engine control module data with an OBD2 scanner to look for faulty sensor readings. 

• Voltages outside of normal parameters confuses the computer, which often triggers the limp mode.

Throttle and Pedal Position Sensor Failures

Two sensors that frequently fail and limit acceleration due to incorrect signals back to the ECU are:

• Throttle position sensors

• Accelerator pedal position sensors

Replace The Defective Sensors That Causes The Acceleration Issues

• If the diagnostics shows that there are failed throttle or pedal position sensors, replace them with new OEM factory equivalent parts immediately. 

• This restores proper data to the engine computer calculations.

• With accurate sensor readings once more, the confused ECU can return to regular operations rather than limiting the speed limits. 

• Therefore, soon, you’ll have your peppy Altima dashing along the highway at peak performances again!

Frequently Asked Questions About Nissan Altima Wont Go Over 20 MPH

Q: Does the Nissan dealership needs to reprogram the computer after new sensors are installed?

A: After installing any new throttle position sensors or accelerator pedal sensors, most mechanics will reset your Altima’s computer and perform an idle relearn procedure. This ensures the electronics fully adapt to the fresh sensors to properly regulate the acceleration signals when the vehicle is moving.

Q: Could faulty spark plugs or bad ignition coils affects the acceleration over 20 mph?

A: Yes, weak ignition coil outputs and failing spark plugs can certainly cause your Altima to struggle to accelerate over 20 miles per hour. To rule them out, conduct an ignition coil resistance check with a multimeter and inspect the spark plug colour. Replacement of worn ignition components often resolves limited top speed issues like this.